Research On Effect Roles Of Motor Variable Speed Running For The Pumping System

Under the condition that electric motor operates at a constant frequency,the drastic fluctuation of the crank torque seriously affects the balance of the pumping system,which increases energy consumption,and reduces service life of equipment.Motor frequency conversion technology has been widely applied in oilfield at present,but the study on effect of frequency conversion is mainly based on field data and experience,lacking theoretical basis.Based on the domestic and foreign simulation achievements on sucker rod pumping system,the motion law and mechanism of four-bar linkage and polished rod before and after crank speed change were analyzed accurately in this paper.Taking sucker rod of two stages for instance,whether the motor frequency has changed or not,one equation is used to describe crank movement and the other to describe sucker rod longitudinal vibration on one dimension.Then a sucker rod pumping system mathematical model were established to analyze and deduce on the two highly coupled equations and iterative methods were used to solve these equations.Compared with the test data,the simulated data is more accurate and improves the working condition obviously.Fuzzy comprehensive evaluation method of multi-factor was adopted,system of evaluation index,as well as subordinate function and its relevant constraint condition were established based on the polished rod load,crank torque,stress and system efficiency of sucker rod string.Aiming at maximizing the value of fuzzy evaluation results,the optimal scheme of frequency conversion was chosen based on the Powell arithmetic.Compared with the simulation method,the data obtained after changing the frequency decreases the polished rod load,the torque of the crank and the peak value of the motor power.The maximum load decreased by 10.5%.The range of stress ratio also improved a lot.For second stage sucker rod,the range of stress ratio was approximate.A statistic analysis was made on the effect after the field application of this technology,it showed that several indexes of pumping unit were improved significantly after the adoption of frequency conversion technology,which provided further verification of this theory.At last,combining theoretical research with field practice,a set of frequency conversion dynamic control software in pumping unit system was developed based on C# and Matlab language.